An ideal glass container has a smooth and flat sealing surface against which the container closure makes a tight seal. Sealing-surface defects such as cracks, scratches, roughness, chips, and other disconformities in the surface may lead to improper seating of the closure, and can prevent hermetic sealing of the container. This in turn leads to spoilage of the container contents. Accordingly, it is necessary to detect such defects on the mouths of these bottles to prevent use of bottles with defects.
Machine vision technology is widely used to inspect the sealing surfaces of glass containers as they are being manufactured or for reuse, to automatically reject defective containers. The inspection of the sealing surface by means of machine vision requires suitable illumination of the sealing surface, and the characteristics of the illumination should allow confident inspection without generating spurious reflections from other portions of the container or its surroundings. Different containers require different illumination techniques for optimum visibility of defects. Two well-known illumination strategies used in sealing-surface inspection are xe2x80x9clight-fieldxe2x80x9d and xe2x80x9cdark-fieldxe2x80x9d illumination. With light-field illumination, the entire sealing surface is visible in the image, and defects appear as light or dark structures on this surface. With dark-field illumination, the sealing surface is not visible, or is barely visible, in the image, but defects appear as bright structures.
Although various methods of detecting defects on a bottle mouth have been proposed, such methods have not provided optimum illumination of the sealing surface. As the defects which may be present and the character of the defects can vary greatly, the illumination of the surface should facilitate identification of any such defects, and yet prior systems have not adequately provided this ability. To detect the widely differing types of defects, it would be desirable to provide illumination which is directed at the surface from differing angles to facilitate defect identification. Further, no such methods are adaptable to different container configurations in a simple and effective manner. It would also be desirable to provide an illumination system and characteristics which allow adaptability to different container configurations and sealing surface characteristics. Other prior art inspection methods and systems have required a container to be rotated 360 degrees under one or more light beams to fully illuminate the sealing surface, but such physical manipulation causes difficulties, as the system is more mechanically complex, and requires an extended dwell time for inspection, which adversely impacts on production in the manufacturing process. It would therefore also be desirable to provide a system and method which allows for inspection without physical manipulation of the container, and at very high production speeds.
The present invention provides an inspection system and methods, and illumination system and methods for dark-field machine vision inspection of containers, such as glass containers or other containers having a sealing surface. The illumination system provides a dual directional helical illumination technique, which enhances the ability to distinguish any defects in the sealing surface area. The illumination system may also provide the ability to adjust the diameter of a circular illumination pattern, so as to allow adjustability and optimization of the illumination characteristics for differing container configurations. For example, containers such as wide-mouth glass containers present difficulties in properly illuminating the surface, and the present invention allows illumination characteristics to be modified to account for such unique containers. For containers having a sealing surface of about 35 mm or larger, it has been difficult to properly illuminate the entire surface for inspection, which the present invention resolves. The use of a helical illumination pattern has also been found to enhance defect visibility in some circumstances, compared to other light-field or dark-field illumination patterns. The simultaneous use of both clockwise and counter-clockwise illumination patterns also improves defect detection. The ability to adjust the diameter of the helical light field allows the illumination to be optimized for any given type of container, and allows rapid changeover from one type of container to another.
In one embodiment of the present invention, these and other advantages are provided by a dark field illuminator comprising a means for projecting a first plurality of collimated light beams in a clockwise helical illumination pattern onto a sealing surface of a container, means for projecting a second plurality of collimated light beams in a counter-clockwise helical illumination pattern onto the sealing surface of the container, and means for recording an image of the illuminated sealing surface. The clockwise and counter-clockwise helical illumination patterns are projected simultaneously onto the sealing surface of the container at a predetermined angle such that the light beams are reflected away from the means for recording an image of the illuminated sealing surface unless a defect is encountered such that at least a portion of the light beam is reflected toward the means for recording an image of the illuminated sealing surface.
In another embodiment of the present invention, these and other advantages are provided by a dark field illuminator comprising a first set of a plurality of mirrored surfaces, a second set of a plurality of mirrored surfaces, and a plurality of light sources each positioned to direct a beam of light toward one of the first set and the second set of the plurality of mirrored surfaces. The mirrored surfaces of the first set of the plurality of mirrored surfaces are positioned to reflect the beams of light at a predetermined angle in a clockwise helical illumination pattern and the mirrored surfaces of the second set of the plurality of mirrored surfaces are positioned to reflect the beams of light at a predetermined angle in a counter-clockwise helical illumination pattern.
In another embodiment of the present invention, these and other advantages are provided by a method for inspecting a sealing surface of a container comprising the steps of a) providing a container having a sealing surface, b) illuminating the sealing surface with a clockwise helical illumination pattern and a counter-clockwise helical illumination pattern at a predetermined angle from an illuminator device, c) recording an image of the illuminated sealing surface, and d) determining whether a defect exists on the sealing surface.
In still another embodiment, these and other advantages are provided by a machine vision system for inspecting a sealing surface of containers comprising an illuminator comprising a plurality of mirrored surfaces which redirect collimated light beams at a predetermined angle in a clockwise and counter-clockwise helical pattern onto the sealing surface of the container, a camera positioned to record an image of the sealing surface when the surface is illuminated by the illuminator, a container positioning sensor which determines when a container sealing surface is properly positioned with respect to the camera and the illuminator, an image inspection system for evaluating whether the image shows a defect on the sealing surface, and a container rejection system which selectively segregates the containers based on whether any defects are detected on the sealing surface. The illuminator directs the light beams onto the sealing surface such that the light beams will be directed away from the camera unless a defect in the sealing surface is encountered wherein at least a portion of the beam will be redirected toward the camera.